Abstract

In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10–50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide.

(a) Absorption (blue line and left axis) and PL (red line and right axis) spectra of CdSe/ZnS core-shell QDs used in this Letter. (b) Fabrication procedure. (c) SEM image after step 4. (d) Microscope image.

(a) PL signal generated in the QD-doped sandwich and nanocomposite waveguides; top pictures depict the cross section of the waveguide signal power at different propagation distances. (b) Waveguided PL spectra in both types of waveguides (1 mm length). Top pictures correspond to the PL signal at the output face of the waveguides.